Mass spectrometric techniques, particularly those requiring the measurement of stable (heavy) nuclide enrichment in biological matrices have become essential tools in the study of nutrition and metabolism under various pathophysiological conditions. The nutrition/metabolic research program within the CNRU has given particular impetus to this area over the past years and it continues to be directed towards a better definition and characterization of the changes in nutrient, fuel and substrate metabolism that accompany various pathophysiological states. A part-time manager will support this core facility together with a well trained full-time technician. The principal functions of the mass spectrometry facility are four: 1. To provide timely and accurate determinations of stable isotope enrichments of tracers and their derivatives in bodily fluids, tissues, and expired air. 2. To assist in development of new methods for isotope analyses of compounds in blood tissues, and urine, as required to meet the needs of the investigators who are participating in the Center Grant research program. 3. To provide quality control for all analysis conducted in support of the research studies that involve use of stale nuclides as tracers. 4. To serve a training function and provide potential new investigators with an opportunity to learn about the application of stable isotope-tracer techniques in metabolic/nutritional research.